If our IP has been banned by a particular WEBSITE, is there anychance to reenter that website using the same computer/internet service

No
Two reasons:

1) You have a good chance of GETTING banned VIA ISP side. Meaning that they will contact your ISP if you continue to cause problems. Your ISP may either a) discontinue your services b) prevent you from any access to that site

2) Anyone who has been banned obviously did something that is undesirable to let back into a website.
In our own moral, we cant really even begin to suggest such a thing. Thanks for the mail

I am sure I have been banned from a forum with out any valid REASON and I never used any thing abusive or illegal and I am sure there is any moral element involved.

anyway thanks for your replyI expect you were banned for the VERY ANNOYING habit of using stupid topic HEADINGS such as "help plssssssssssssssssss..........." which make some people very angry.

The best thing you can do is this:

Email the webmaster.
Find a contact email on the main site, or try the following email address:

[emailprotected]
(replace thesitehere.com with the website you were visiting)
Many webmasters make sure that there is a regular webmaster email available.